Submerged combustion melters and methods

ABSTRACT

A submerged combustion melter  10  is arranged with a vertical melting chamber  11 , which may be cylindrical, and at least five submerged combustion burners  21 - 26  in the bottom base  13 , the burners so spaced apart from each other and from the walls and angled from the vertical that in use a toroidal flow pattern can be achieved, providing intensive mixing. The claims also pertain to a method of melting a vitrifiable material from solid batch by submerged combustion melting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/908,360, filed Jan. 28, 2016, which is a U.S. national counterpartapplication under 35 U.S.C. § 371 of International Application SerialNo. PCT/EP2014/066443, filed Jul. 30, 2014, which claims priority to GBApplication Serial No. 1313654.4, filed Jul. 31, 2013, the entiredisclosures of which are expressly incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to submerged combustion melters, notablyfor melting vitreous or vitrifiable material, and to processes using asubmerged combustion melter.

BACKGROUND

Vitreous materials are generally manufactured from a mixture of rawmaterials, for example silicates, basalt, limestone, soda ash and otherminor constituents which are introduced into a melter and melted into aviscous liquid state at temperatures in the order of 1250 to 1500° C.;the melt is then supplied to a forming process. Depending on theintended use of the melt, for example for manufacture of flat glass,hollow glass, continuous fibers for reinforcement purposes or fibers forinsulation purposes, an appropriate further melt refining step may berequired upstream of the forming process. The chemical composition ofthe melt and its physical properties are selected as a function of theintended use and the forming process.

Conventional glass melters comprise an energy supply from above a glassmelt surface, for instance from burners generating a flame in a spacebetween the glass melt surface and a crown of the melter, whereby heatis transferred to the glass melt by the flame itself and by radiationfrom the crown material. Raw batch material to be melted is loaded atthe top of the glass melt in the melter and heat is transferred from themelt to the batch material which is incorporated into the melt.

In some glass melters, energy is supplied by electrically heatedelectrodes arranged below the surface of the melt; such electrodes mayprovide the only heat source or be used in combination with burners.

A further type of glass melter has one or more burner nozzles arrangedbelow the surface of the melt such that the burner flame and combustionproducts pass through the melt. This arrangement is referred to assubmerged combustion.

Glass melters used to manufacture stone wool insulation havetraditionally been cupola furnaces.

SUMMARY

According to one of its aspects, the present invention provides asubmerged combustion melter as defined in claim 1. Other independentclaims define other aspects of the invention. Dependent claims definepreferred and/or alternative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a horizontal cross-sectional plan view of a melter;

FIG. 2 shows a vertical section through the melter of FIG. 1;

FIG. 3 shows a schematic representation of the burner layout; and

FIG. 4 shows a schematic representation of a preferred toroidal flowpattern.

DETAILED DESCRIPTION

One or more aspects described in the following patent applications,which also relate to submerged combustion melting and/or melters, may beused in respect of the inventions of the present patent application andeach of the following patent applications is hereby incorporated byreference:

Name of Priority Application applicant claimed Our ref International PCTpatent Knauf GB 1313653.6 P0524/PCT application PCT/EP2014/ InsulationKMRecup 066440 filed on 30 Jul. 2014 International PCT patent Knauf GB1313656.9 P0554/PCT application PCT/EP2014/ Insulation KMScrap 066441filed on 30 Jul. 2014 International PCT patent Knauf GB 1313652.8P0523/PCT application PCT/EP2014/ Insulation KMburn 066442 filed on 30Jul. 2014 International PCT patent Knauf GB 1313651.0 P0522/PCTapplication PCT/EP2014/ Insulation KMMod 066444 filed on 30 Jul. 2014

As used herein the term “vertical central melting chamber axis” meansthe vertical or substantially vertical symmetry axis of the meltingchamber. The melting chamber may have a circular horizontal crosssection; it may be cylindrical. Alternatively, the melting chamber mayhave a polygonal horizontal cross section, notably in the form of aregular polygon; the polygon may have six, seven, eight, nine, ten ormore sides. Each of these shapes has a defined central symmetry axis.The horizontal cross section of the melting chamber may be elliptical oroval; in this and in similar cases the vertical central melting chamberaxis is the axis passing through the center of a circle in which therelevant horizontal cross sectional shape is inscribed.

The nozzle outlets of the submerged combustion burners may be arrangedat the same vertical height within the melting chamber i.e. in the samehorizontal plane. Alternatively, they may be arranged at differentvertical heights. The burner positioning plane thus is defined as beingarranged at a “weighted average distance with respect to each of thenozzle outlets”. That means that the average distance is weighted overthe number of burners.

The term “weighted burner axis-periphery distance in the melter” shouldbe understood to mean the weighted distance between the central burneraxis as defined and the inner periphery of the melting chamber. In caseswhere the burner axis and the peripheral wall(s) of the melting chamberare parallel, this is simply the distance between the burner axis andthe peripheral wall. In other cases, the “weighted burner axis-peripherydistance in the melter” is the arithmetic mean distance over the heightof the melting chamber between the burner axis and its closest portionof peripheral wall.

The melter may be adapted and/or configured to sinter and/or melt rawmaterials. It may be a “glass melter”, that is to say a melter adaptedand/or configured to melt glass-like materials including materialsselected from glass, vitreous materials, stone and rock. A glass meltermay be used to manufacture flat glass, hollow glass, glass fibers,continuous fibers for reinforcement purposes, mineral fibers forinsulation purposes, mineral wool, stone wool or glass wool. The meltermay be used to transform raw materials to manufacture frits, cementclinker, notably alumina cement clinker, or abrasives, notably abrasivesproduced by melting. The melter may be used to transform raw materials,notably by vitrification, for example: vitrification of medical wastes;vitrification of ash, notably from incinerators; vitrification ofpowders, for example dusts from cast iron or other metal foundries;vitrification of galvanic sludge, tannery sludge or mining industrywaste; disposal of waste, notably by vitrification, for example, ofpolluted soil, soil polluted by heavy metals or tar, clay filters,sludge, activated carbon, radioactive waste, slags containing lead orzinc, refractories, notably refractories containing chromium.

Particularly in the case of a glass melter, the raw materials maycomprise: silicates, basalt, limestone, soda ash, zeolite catalyst,spent catalyst, spent pot liner, refractory materials, aluminum dross,aluminium melting scum, sand based fire extinguisher waste, sludge,galvanic sludge, clinker, waste materials, ash and combinations thereof.

The melt within the melter during operation may reach a temperature,notable a temperature at which it is removed from the melter, which isat least 1100° C., at least 1200° C. or at least 1250° C. and which maybe no more than 1650° C., no more than 1600° C., no more than 1500° C.or no more than 1450° C.

In the case of a glass melt, the composition of the melt produced maycomprise one or more of:

Possible melt Preferred melt composition composition (% weight) (%weight) SiO₂ 35-70  40-65 Al₂0₃ 5-30 15-25 CaO 5-20  5-12 MgO 0-10 1-7Na₂O 0-20  5-18 K2O 0-15  0-10 Fe₂O₃ (total iron) 0-15 0.5-10  B2O3 0-100-5 TiO₂ 0-5  0-2 BaO P₂O₅ 0-3  0-2 MnO 0-3  0-2 Na₂O + K₂O 5-30  5-20(alkali metal oxide) CaO + MgO 5-30  5-20 (alkaline earth metal oxide)Si02 + Al2O3 50-85  60-80

The boron content of glass produced, expressed as B2O3, may be ≥1 w %,≥2 w %, ≥3 w %, ≥5 w % and/or ≤20%, ≤18%, ≤15% or ≤10 w %.

The melters provide an efficient configuration for melting materials,notably vitrifiable materials, with low energy consumption and lowcapital costs and provide desirable melt characteristics includinghomogeneity in terms of temperature distribution and composition of themelt, leading to improved end product quality. They also allow meltingof a wide variety of materials, notably vitrifiable material, includingraw material (for glass formation these may be for example silicates,basalt, limestone, soda ash and other minor constituents) and wastematerial or ashes, and provide high flexibility in controlling processparameters.

In preferred configurations such melters improve the absorption of freshraw material within the melt and the efficiency of the transmission ofheat to fresh raw material, notably when added at the top of the meltwhilst any bypass of raw material through the melter is largely avoidedor at least further reduced. This provides a combination of efficientmelting, notably of vitrifiable material, and hence to smaller meltersfor a given output flow whilst also improving melt homogeneity in termsof temperature profile and composition.

The height of a melt pool within the melter, especially when the meltingchamber is substantially cylindrical, preferably with an internaldiameter of the melting chamber of 1.5 m to 3 m, more preferably 1.75 to2.5 m, may be:

≥ about 0.75 m, ≥ about 0.8 m, ≥ about 0.85 m or ≥ about 0.9 m; and/or≤ about 2.2 m, ≤ about 2 m, ≤ about 1.8 m, or ≤ about 1.6 m.

Preferably, the majority of the mixing of the melt occurs in a centralmelting zone which may be substantially cylindrical and which may have adiameter which is: at least 25 cm, at least 30 cm, at least 40 cm, atleast 50 cm, at least 60 cm or at least 70 cm and or no more than 200cm, no more than 180 cm or no more than 160 cm.

The melter, or at least the melting chamber, may be liquid cooled. Forexample, it may comprise a double walled construction comprising aninner wall forming the periphery of the melting chamber and a spacedouter wall which together define a passage through which cooling fluid,notable water, may pass. Preferably, the melting chamber and/or theperiphery of the melting chamber does not comprise refractory materials.

In preferred embodiments, the configuration of the melter enablesgeneration of a toroïdal melt flow pattern in which melt is ascending atproximity of the relevant central burner axis and converging inwardlytowards the vertical melter axis at the melt surface and downwardly atproximity of said vertical melter axis, within an essentiallycylindrical space having the central melting zone as a basis.

The submerged combustion melter may be equipped with 5 to 10 submergedcombustion burners, more preferably 6 to 8 burners, depending on themelter dimensions, burner dimensions, operating pressure and otherdesign parameters. Notably in the case of providing a melt for glassfiber, glass wool or stone wool production, the melting chamber may becylindrical and may have an internal diameter of 1.5 to 3 m, preferably1.75 to 2.5 meters.

The spacing between adjacent burners should be selected as a function ofburner design, operating pressure and other parameters. Too small adistance between burners may lead to joining of the flames fromindividual burners, a phenomenon that should be avoided. Preferably, theadjacent burner spacing is about 1.5 to 2.5, more preferably 1.75 to2.25, most preferably about twice the burner axis-periphery distance.

Advantageously, adjacent burners are arranged at a spacing between themof about 250-1200 mm, preferably about 500-900 mm, more preferably about600-800, even more preferably about 650-750 mm.

According to a preferred embodiment, the burners are arranged at asuitable burner axis-periphery distance which favors the relevant flowdescribed above and avoids flame attraction to the melter side walls.Advantageously, the burner axis-periphery distance is about 250-750 mm.Too small a distance between burners and side wall may damage and/orunnecessarily stress the side wall and/or be inefficient for heattransfer to the melt. A certain melt flow between a burner and theperiphery of the melting chamber may not be detrimental and in somecases is desirable. Nevertheless, too a large distance between a burnerand the periphery of the melting chamber tends to generate undesirablemelt flows and may result in dead zones which mix less with the melt inthe center of the melter; this can lead to reduced homogeneity of themelt. Preferably, the distance between each burner and the periphery ofthe melting chamber is arranged such that a layer of melt, for example alayer having a thickness of between about 2 mm and 20 mm, builds up as asubstantially stationary boundary layer at the periphery. Such aboundary layer provides a protecting layer at the periphery of themelting chamber and facilitates operation without refractory linings,notably when the melter chamber periphery is liquid cooled.

Particularly in the case of a glass melter, each burner is preferablysupplied with a combustible gas, notably comprising hydrocarbon(s), forexample natural gas, and an oxygen containing gas, notably oxygen,technical grade oxygen (for example gas having an oxygen content of atleast 95% by weight) or oxygen enriched air. Preferably, the combustiblegas and the oxygen containing gas are supplied separately to the burnerand combined at the burner and/or at nozzle(s) of the burner.Alternatively, other fuel types, for example liquid fuel or solidpulverized fuels, may be used, notably for waste vitrification.

In preferred embodiments, a toroidal melt flow pattern in the melt isgenerated in the melting chamber. The term “toroidal flow pattern” meansthat the velocity vectors of the moving fluid material form acirculation pattern in which they fill cross-sections of an essentiallyhorizontal toroid which has as its central axis of revolutionsubstantially the vertical central melting chamber axis and as its outerdiameter approximately the circumference defined by the central burneraxes, with material flowing from the outside toward the central melteraxis at the melt surface. Such toroidal flows entrain fresh raw materialcentrally and deeply into the glass melter in the proximity of thecentral melter axis within a substantially cylindrical space having thecentral melting zone as basis, and improve the efficiency intransmitting heat to the fresh raw material in order to melt the rawmaterials quickly and easily and further enhance homogeneity of themelt. Preferably, the melt in the melter comprises a single suchtoroidal flow pattern

The melt and/or the raw materials within the melter, at least at oneportion of the melter and notably at the central melting zone, may reacha speed which is ≥0.1 m/s, ≥0.2 m/s, ≥0.3 m/s or ≥0.5 m/s and/or whichis ≤2.5 m/s, ≤2 m/s, ≤1.8 m/s or ≤1.5 m/s.

The raw material to be melted may advantageously be introduced at orabove the melt surface. The flow pattern of the melter allows forefficient absorption of raw material into the melt and thus efficientheat transfer to the fresh raw materials which are incorporated into themelt.

Each burner or of a group of burners, for example opposed burners, maybe individually controllable. As a result, one or more burners close toa raw material discharge may be controlled at different, preferablyhigher gas speeds and/or pressures than adjacent burners, thus allowingfor improved heat transfer to the fresh raw material that is beingloaded into the melter. Higher gas speeds may be required onlytemporarily, that is, in the case of batch wise loading of fresh rawmaterial, just during the time period required for absorption of therelevant load into the melt contained in the melter of the invention. Itmay also be desirable to control the burners that are located close tothe melt outlet at a lower gas speed/pressure in order to control theoutlet of the melt.

Each central burner axis may be slightly inclined from the vertical, forexample by an angle which is ≥1°, ≥2°, ≥3° or ≥5 and/or which is ≤30°,preferably ≤15°, more preferably ≤10°, notably towards the center of themelter. Such an arrangement may improve the flow and direct melt flowaway from the outlet opening and towards the center of the melter and/orfavor a toroidal flow pattern. Preferably, for one or more burners thereis an increase of at least 1% in the burner axis-periphery distancebetween the burner positioning plane and the top of the melter.

Advantageously, for one or more burners the central burner axis forms aswirl angle of at least 1° with respect to a plane which isperpendicular to the burner positioning plane, passes through thevertical central melting chamber axis and passes through the burnerposition. The swirl angle may be ≥1°, ≥2°, ≥3°, ≥5° and/or ≤30°, ≤20°,≤15° or ≤10°. Preferably, the swirl angle of each burner is about thesame. This arrangement of burners may be used to impart a tangentialspeed component to the combustion gases, thus imparting a swirlingmovement to the melt flow and further improving the mix of raw materialand the homogeneity of the melt.

The melter preferably has a substantially cylindrical periphery, but mayalso show other shapes, for example an elliptical cross section orpolygonal cross section showing more than 4 sides, preferably more than5 sides, the essence being that in preferred embodiments the arrangementgenerates a toroidal melt flow as described above. It will beunderstood, that the more uniform the distances are between burners andside wall, the more uniform the toroidal melt flow will be.

The fresh raw material may be loaded by means of a feeder.Advantageously, the raw material is loaded through an opening into themelting chamber positioned above the melt surface. The raw material maybe loaded batchwise. A batch of raw material may be comprised between 20and 50 kg. In the case of a melter showing a production rate of approx.70000 kg/day, the batch loading frequency may vary between 20 and 50kg/min. It is preferred, however, to feed the raw material substantiallycontinuously or in a manner close to being continuous. For reasons ofprocess control, including temperature and flow control and homogeneityof the melt, it is preferred to feed small batches at high frequencyrather than large batches at low frequency. Said opening is preferablycloseable, for example by a piston or actuator; this may be used tominimize heat loss and/or escape of fumes through the feeder. Rawmaterial may be prepared as appropriate for the relevant melt to beobtained and loaded into an intermediate chute. When the opening intothe melting chamber is opened, the raw material may be introduced intothe melter, notably in an opposite direction to escaping fumes and thuspartially preheated as it falls onto the melt surface. Preferably, thefeeding opening is arranged in a recess provided in the melter peripheryabove the melt surface, such that the raw material falls on the meltsurface within a loading zone at a distance from the melter periphery.

Melt may be withdrawn continuously or batch wise from the melter, forexample from a position at or towards the bottom of the melter. In caseswhere the raw material is loaded close to the melter wall, the meltoutlet is preferably arranged at the melter periphery opposite the rawmaterial inlet. In the case of discontinuous discharge of melt, thedischarge hole is preferably controlled, for example using a ceramicpiston.

One or more of the burners may be tube in tube burners which are alsoknown as concentric tube burners. The central burner axis of one or moreof the submerged combustion burners advantageously comprises the centralaxis of concentric tubes of a tube-in-tube burner. The submergedcombustion burners inject high pressure jets of the combustion productsinto the melt sufficient to overcome the pressure of the melt and tocreate forced upward travel of the flame and combustion products. Thespeed of the combustion and/or combustible gases, notably at the exitfrom the burner nozzle(s), may be ≥60 m/s, ≥100 m/s or ≥120 m/s and/or≤350 m/s, ≤330 m/s, ≤300 or ≤200 m/s. Preferably the speed of thecombustion gases is in the range of about 60 to 300 m/s, preferably 100to 200 m/s, more preferably 110 to 160 m/s.

According to a preferred embodiment, the melting chamber's peripheralwalls consist of double steel walls separated by a circulating coolingliquid, preferably water. Particularly in the case of a cylindricalmelting chamber, such assembly facilitates construction of the meltingchamber and resistance to high mechanical forces and stresses. Acylindrical shape of the melter allows for optimization of the balanceof stress on the outside wall. Preferably, as the walls are cooled,preferably water cooled, melt solidifies and forms a protective layer onthe inside of the melter wall. In preferred embodiments the meltingchamber does not require internal refractory lining and therefore avoidsthe need for associated costs and maintenance. In addition, in suchcases the melt is not contaminated with undesirable components ofrefractory material eroded from the internal refractory lining. Theinternal face of the melter wall may advantageously be equipped withtabs or pastilles or other small elements projecting towards the insideof the melter. These may help constituting and fixing a layer ofsolidified melt on the internal melter wall which plays the role of alining generating a thermal resistance and reducing the transfer of heatto the cooling liquid in the double walls of the melter.

The submerged combustion melter of the invention may be equipped withheat recovery equipment. For example, hot fumes exhausted from themelting chamber may be used to preheat raw material and/or a portion oftheir thermal energy may be recovered using a heat exchanger and/ortheir thermal energy may be used for other purposes in upstream ordownstream equipment of a production line, e.g. a production line forinsulating fiber products. Similarly, thermal energy from any coolingliquid circulating between hollow walls of the melting chamber may berecovered for heating or other purposes.

The disclosed method and melter are particularly suitable to melt allsorts of vitrifiable material in an efficient way, with reduced energyconsumption and at reduced maintenance costs. A melter as per theinvention is thus particularly attractive for use in a production linefor mineral fiber products, for example glass fibers, glass wool andstone wool manufacturing. Particularly in the case of mineral wool fiberproduction, the output is preferably taken directly to fiberizationwithout a refining step.

An embodiment of the invention is described in more details below, byway of example only, with reference to the accompanying drawings ofwhich:

FIG. 1 is a horizontal cross-sectional plan view of a melter;

FIG. 2 shows a vertical section through the melter of FIG. 1;

FIG. 3 is a schematic representation of the burner layout; and

FIG. 4 is a schematic representation of a preferred toroidal flowpattern.

The glass melter 10 illustrated in FIGS. 1, 2 and 3 comprises a meltingchamber 11, that is to say a portion of the melter 10 adapted to retainand melt a heated melt 17, for example of a composition formanufacturing stone wool or glass wool fiber, and an upper chamber 90.

The illustrated melting chamber 11 is cylindrical and has a verticalcentral melting chamber axis 7, a periphery 12 defined by its internalcircumference which has a diameter of about 2 m, a base 13 forming thelower ender of the cylinder and an open end at the upper end of thecylinder which communicates with the upper chamber 90.

The upper chamber 90 is provided with:

-   -   a chimney 91 for evacuation of the gasses from the melting        chamber 11;    -   baffles 92, 93 that block access to any melt projections which        may be thrown up from the surface of the melt 14; and    -   a raw material feeder 15 arranged at the level of the upper        chamber 90 to load fresh raw material into the melter 10 at a        batch introduction position 101 located above a surface 18 of        the melt and close to the peripheral side wall 12 of the melter.

The feeder 15 comprises a screw or other horizontal feeder whichtransports a raw material mix to a hopper which may be opened and closedby a piston.

The melter has a double steel peripheral wall 19 having a coolingliquid, preferably water, circulating through its interior at a flowrate which is sufficient to maintain a desired temperature of the melterand of the cooling fluid and withdraw energy from the inside peripheralwall 12 such that a portion of the melt can solidify or partiallysolidify on the internal peripheral wall to form a boundary layer.

If desired the melter may be mounted on dampers to absorb vibrations.

Six submerged burners 21, 22, 23, 24, 25, 26 are arranged, equallyspaced around a substantially circular burner line 27 which isconcentric with the central vertical melting chamber axis 7 and has adiameter of approximately 1.4 m. Each submerged combustion burner has arespective central burner axis 31,32,33,34,35,36 and one or more outletnozzles 41,42,43,44,45, 46 from which flames and/or combustion fluidsare projected in to the melt 17. Each burner is positioned at asubstantially identical adjacent burner spacing 512, 523, 534, 545, 556,561 with respect to each of its two closest adjacent burner positions.The burner nozzles 41, 42, 43, 44, 45, 46 in the illustrated embodimentare arranged to project slightly above the base 13 of the meltingchamber, each at the same vertical height as a burner positioning plane14.

Each central burner axis 31,32,33,34,35,36 has a respective burner axiscircle 71,72,73,74,75,76 which extends around the central burner axisand has a radius r1,r2,r3,r4,r5,r6 which is substantially equal to thedistance between the central burner axis and the peripheral wall 12 ofthe melting chamber. These burner axis circles define a central zone 70at the positioning plane 14 having a diameter of at least 250 mm.

The melt 17 may be withdrawn from the melting chamber through acontrollable outlet opening 16 located in the melter chamber peripheryside wall 12, close to the melter bottom 13, substantially opposite theraw material feeder 15.

The submerged burners 21,22,23,24,25,26 are tube in tube burners,sometimes referred to as concentric pipe burners, operated at gas flowor speed in the melt of 100 to 200 m/s, preferably 110 to 160 m/s. Theburners generate combustion of fuel gas and air and/or oxygen within themelt. The combustion and combustion gases generate high mixing and highrates of heat transfer within the melt before they escape from the meltinto the upper chamber 90 and are exhausted through the chimney 91.These hot gases may be used to preheat raw material and/or the fuel gasand/or oxidant (air and/or oxygen) used in the burners. The exhaustfumes are preferably cooled, for example by dilution with ambient air,and/or filtered prior to release to the environment.

It is preferable that the arrangement generates a toroidal melt flow asillustrated in FIG. 4 in which the melt follows an ascending directionclose to the central burner axis of each submerged burner, flowsinwardly towards the vertical central melting chamber axis 7 at the meltsurface 18 and then flows downwards in an substantially cylindricalportion of the melting chamber which projects along the vertical centralmelting chamber axis 7 from the central melting zone 70. Such a toroidalflow generates high mixing in the melt, ensures good stirring of themelt and absorption of fresh raw material and allows for appropriateresidence time of the material in the melter, thereby avoiding prematureoutflow if insufficiently melted or mixed raw materials.

The burners generate an ascending movement of melt in their proximityand a circulation within the melt. In one preferred embodiment, eachburner axis is vertically oriented or inclined at an angle of no morethan 15° from vertical, advantageously towards the center of the melter,in order to favor the generation of toroidal flow as taught above.

To further improve homogeneity of the melt, one or more burners mayimpart a tangential velocity component to its combustion gases, henceimparting a swirling movement to the melt flow, in addition to thetoroidal flow pattern described above. For that purpose, the centralburner axis of one or more burners may form a swirl angle of at least 10with respect to a plane which is perpendicular to burner positioningplane 14 and which passes through the vertical central melting chamberaxis 7 and the burner position.

The melter may be equipped with an auxiliary burner (not shown) notablyfor temporary use for example for preheating the melter when starting,in the case of malfunction of one of the submerged burners describedabove or in other cases where additional heat is temporarily required.The auxiliary burner is advantageously mounted on a rail so that it canbe guided into an opening provided in the melter peripheral wall 12, theopening being closed when the auxiliary burner is not in use.

The internal melter wall 12 advantageously comprises a multitude of tabsor pastilles (not shown) projecting inside the melter chamber 11. It isbelieved these projections favor the formation and fixation of asolidified melt layer on the cooled wall 12, which constitutes aninsulating layer. In the case of a glass melt for instance, glasssolidifies on the cooled wall and forms an insulating boundary layer.Glass is thus melted in glass and the melt is not contaminated witherosion residues of any refractory material.

A melter according to the invention is particularly advantageous in aglass fiber, glass wool or stone wool production line because itsefficiency provides for low energy consumption and its flexibilityfacilitates changes of raw material composition. Ease of maintenance andlow capital costs of the melter are also of major interest in buildingsuch a production line. The same advantages also make the inventionmelter the melter of choice in waste and ash vitrification processes.

1.-11. (canceled)
 12. A method of providing a molten vitrifiablematerial comprising the steps of: introducing solid batch material intoa melter; and melting the solid batch material in the melter bysubmerged combustion to provide the molten vitrifiable material withinthe melter; wherein during the melting step an essentially toroidal meltflow pattern is generated in the melt of vitrifiable material,comprising a major centrally inwardly convergent flows at the meltsurface, the central axis of revolution of the torroidal flow beingessentially vertical.
 13. The method of claim 12 wherein the melt movesdownwardly in the center at proximity of the axis of revolution and isrecirculated in an ascending movement back to the melt surface, thusdefining an essentially toroidal flow pattern.
 14. (canceled)
 15. Themethod of claim 12 wherein velocity vectors of the moving melt form acirculation pattern in which said velocity vectors fill cross-sectionsof an essentially horizontal toroid.
 16. The method of claim 12 whereinthe melt in the melter comprises a single such toroidal flow pattern.17. The method of claim 12 wherein the melter has a substantiallycircular cross-section and the central axis of revolution of thetoroidal flow pattern essentially corresponds with the melter axis. 18.The method of claim 12 for the manufacture of flat glass, hollow glass,glass fibers, continuous fibers for reinforcement purposes, mineralfibers for insulation purposes, mineral wool, stone wool or glass wool.19. The method of claim 12 wherein the solid batch material comprisessilicates, basalt, limestone, soda ash, zeolite catalyst, spentcatalyst, spent pot liner, refractory materials, aluminum dross,aluminum melting scum, sand based fire extinguisher waste, sludge,galvanic sludge, clinker, waste materials, ash and combinations thereof.20. The method of claim 12 wherein the composition of the melt producedcomprises composition (% weight) SiO₂ 35-70  Al₂0₃ 5-30 CaO 5-20 MgO0-10 Na₂O 0-20 K₂O 0-15 Fe₂O₃ (total iron) 0-15 B₂O₃ 0-10 TiO₂ 0-5  BaOP₂O₅ 0-3  MnO 0-3  Na₂O + K₂O 5-30 (alkali metal oxide) CaO + MgO 5-30(alkaline earth metal oxide) SiO₂ + Al₂O₃ 50-85 


21. The method of claim 20 wherein the composition of the melt producedcomprises composition (% weight) SiO₂ 40-65 Al₂0₃ 15-25 CaO  5-12 MgO1-7 Na₂O  5-18 K₂O  0-10 Fe₂O₃ (total iron) 0.5-10  B₂O₃ 0-5 TiO₂ 0-2BaO P₂O₅ 0-2 MnO 0-2 Na₂O + K₂O  5-20 (alkali metal oxide) CaO + MgO 5-20 (alkaline earth metal oxide) SiO₂ + Al₂O₃ 60-80


22. The method of claim 12 wherein the boron content of the glassproduced, expressed as B₂O₃, is ≥1 w %, ≥2 w %, ≥3 w %, ≥5 w % and/or≤20 w %, ≤18 w %, ≤15 w % or ≤10 w %.
 23. The method of claim 12 whereinhot fumes from the melting chamber are used to preheat raw materialand/or a portion of their thermal energy is recovered.